Patent GB-670050-A (GB)
Title: Improvements in and relating to automatic electric circuit opening devices
IPC: H01H73/34
Filed: 1949-08-25
Abstract: 670,050. Automatic circuit - breakers. BRITISH THOMSON-HOUSTON CO., Ltd. Aug. 25, 1949. [Sept. 1, 1948] No. 22116/49. Class 38 (v). A circuit-breaker, as disclosed in Specification 650,509, used for isolating a branch or feeder and operating in conjunction with a main automatically-reclosing circuit-breaker, is provided with means whereby a predetermined number of overcurrent' impulses must . pass through'it before it can isolate the branch. The electromagnet armature 34 has an extension plate 46 slidable between guide plates 48, 49 and a further plate, Fig. 2 (not shown) rivetted together and secured by brackets 51 to the magnet frame 32. Plates 48, 49. are spaced apart on one side of the extension 46 and have elongated notches 52, 53, respectively, staggered relatively to each other, and springs 58, 59 on the plates 48, 49 have their free ends opposite the respective upper edges 54, 55 of the notches 52, 53. A dog 60 comprising a lever pivoted at 63 to the armature extension 46 has ears 61, 62 provided with pins 64, 65 and normally occupies the position shown in Figs. 1, 6, with ear 61 in notch 52. A conventional time delay means 66 connected by a vertical rod 67 to a lateral projection of the extension 46, retards downward movement of the armature 34. On fault, magnet 31. pulls the armature 34 and its extension 46 upwardly whereby the ear 61 engages the notch-end 54, and the movement is thus arrested. before a lip 45 on the armature 34 can engage an arm 36 to unlatch the circuitbreaker. During this movement, the pin 64 is enabled to deflect the spring 58 owing to the speed of travel and inertia of the dog 60. A recloser in series with the breaker is also operated by the fault and opens the circuit so that the magnet 31 is de-energized and the armature 34 drops slowly, whereupon the stressed spring 58 swings the dog about its pivot 63 and the ear 62 engages notch 53. The. arrangement is such that before the ear 62 reaches the sloping lower end 57 of the notch 53, the recloser recloses the circuit. and if the fault still persists the armature is lifted again until the ear 62 engages the upper notch-end 55, the spring 59 being deflected by the pin 65. In this higher position of the armature 34, the latter is still not sufficiently raised for unlatching the breaker. On subsequent opening of the recloser, the armature again falls and the stressed spring 59 swings the dog 60 counter-clockwise so that its ear 61 engages the edge of the guide plate 48 at a point above a sloping edge 70. Before the ear 61. reaches the edge 70 the circuit is reclosed a second time by the recloser and if the fault yet persists the armature is raised its full extent to unlatch the breaker which, upon a subsequent and third interruption of the recloser, opens as described in the abovementioned Specification 650,509. If, after the first reclosure, the fault is removed, the armature will move down into its original position and the breaker will not be opened. By using fewer notches or by adding more, the breaker may open on the second or fourth interruption of the recloser; hence several breakers, graded as regards the number of interruptions of the recloser required to open them, may be used to isolate a main feeder, a branch, and a subbranch of the protected circuit. The breaker may alternatively operate in conjunction with a multi-shot fuse device.